1. Field of the Invention
A present invention relates to a manufacturing method of a liquid crystal display panel, and its manufacturing apparatus. In particular, it relates to a manufacturing method of a liquid crystal display panel using a liquid crystal dripping and panel pasting method, and a liquid crystal dripping device to be used for the method.
2. Description of the Related Art
Since it has advantages, such as thin shape, light weight, and low power consumption, the liquid crystal display panel is widely used as a display of AV equipment or OA equipment.
The liquid crystal display panel is sandwiching the liquid crystal between a pair of substrates disposed face to face each other. The liquid crystal display panel provides a pair of electrodes, and controls an alignment direction of a liquid crystal molecule by the electric field generated between electrodes. The liquid crystal display panel displays images by modulating the light irradiated through the liquid crystal display panel in the alignment direction of the controlled liquid crystal molecule.
In the manufacturing method of the liquid crystal display panel, there is a method generally named a liquid crystal filling method as a method of filling the liquid crystal between the pair of substrates disposed face to face each other. The liquid crystal filling method has the following typical methods.
One method is a dipping method for filling the liquid crystal by using pressure difference in a vacuum chamber. In this method, an alignment and pasting of the pair of substrates are to be performed. For pasting each substrate which opposes together, a sealing material is applied on the surface of the substrate except for the area used as a liquid crystal filling port, and the pair of substrates pasted together is called “a cell”. Then, this cell is put into the vacuum chamber and the pressure inside of the vacuum chamber is decreased to a low pressure state. Next, the liquid crystal filling port of the cell is dipped into the liquid crystal, and returning the pressure of the inside of the vacuum chamber to an atmosphere pressure state. Then, the liquid crystal is sucked up inside of the cell by pressure difference.
In another method, the cell is provided with two ports, a filling port and an exhausting port. The filling port is dipped into the liquid crystal and air inside of the cell is exhausted from the exhausting port, and as the result, the liquid crystal is sucked up inside of the cell by pressure difference.
An example of the manufacturing method of the liquid crystal display panel by the liquid crystal filling method is described with reference to FIG. 7.
FIG. 7 is a flow diagram showing a part of manufacturing process of the liquid crystal display panel by the conventional liquid crystal filling method.
As a pair of substrates to be used for the cell, a TFT substrate on which switching elements, such as TFT (Thin Film Transistor), are formed in matrix form, and another substrate as a counter substrate on which a color filter and a black matrix are formed are used, and processes are to fill the liquid crystal inside of the cell.
First, by using a printer, provide coating of solution of polyimide, as a material of an alignment layer, on a surface of the TFT substrate and also on a surface of the counter substrate, then performs pre-baking using heating equipment such as a hot plate oven or an IR oven. After pre-baking, performs main baking for carrying out heating dehydration condensation of the polyimide coating film, and forms the alignment layer of uniform thickness (S710, S720).
Next, rubbing process is to be performed for respective alignment layers on both substrates by a rubbing roller which rubs over the surface of the alignment layer in a same direction by a rubbing cloth (S711, S721).
More over, in order to remove the residue on the surface of the substrate, respective substrates are washed by ultrasonic cleaning, jet spray cleaning, which uses warm ultra-pure water or an alcohol. Then, puts the substrates into a drying equipment and dries the substrates with a hot blast circulation or an infrared heating (S712, S722).
Next, using a screen printing method with a heat curing resin, forms the seal patterning for specifying an area, in which the liquid crystal is to be filled, except for a portion of the liquid crystal filling port on one of the substrates of the pair, (it is assumed that the TFT substrate is used for this substrate as an example), and after this, an AG coating is applied (S713, S714).
Spray spacers, such as polymer beads or silica beads, on the other substrate of the pair substrates by a spacer sprayer with a wet type method or a dry type method, and makes them fix (S723, S724).
Next, carries out panel alignment for both substrates of the pair which have performed the above-mentioned processing, and pastes them together (S730).
The substrates of the pair pasted together are pressed from both outsides, the seal material is to be crushed, and a desired gap between two substrates is formed, then the substrates are baked at a predetermined temperature (S731).
Thus, after seal baking process, cuts the substrates of the pair in a predetermined portion of the outside of the seal material (S732).
Next, after drying the substrates of the pair pasted together (S733), holds the substrates in a vacuum system, and decompresses the inside of the vacuum system, which causes a space produced in a gap part between the substrates being decompressed.
Then, the liquid crystal filling port of the substrates pasted together is dipped into liquid crystal, and after dipping, returns the inside of the vacuum system back to the atmosphere pressure state. By this process, the liquid crystal is filled in the gap part between substrates by pressure difference (S734).
After the liquid crystal has been filled in the gap, ultraviolet curing resin is poured into the liquid crystal filling port for end sealing. An ultraviolet rays is glared for curing ultraviolet curing resin to provide end sealing of the liquid crystal filling port, and a liquid crystal display panel (S735) is formed.
The liquid crystal filling method which was mentioned above has such disadvantages as taking long time for filling the liquid crystal through very small liquid crystal filling port (a tiny hole), and requiring a large amount of liquid crystal for dipping the liquid crystal filling port into liquid crystal.
Therefore, another method called a liquid crystal dripping and panel pasting method is used in recent years.
The liquid crystal dripping and panel pasting method applies the seal material to one substrate, drips liquid crystal onto the substrate and pastes another substrate on it in an ordinary atmosphere or a decompressed atmosphere state. It is the method of stiffening the seal material by pressurization or a pressure difference between decompressed atmosphere state and normal atmosphere state. This liquid crystal dripping and panel pasting method can shorten working hours substantially since the liquid crystal is directly dripped on the substrate. Also, it has an advantage of reducing amount of costly liquid crystal because a necessary minimum liquid crystal is enough to be used.
With reference to FIG. 8, the liquid crystal dripping and panel pasting method which drips the liquid crystal under ordinary atmosphere state will be described.
FIG. 8 is a figure of flow showing a part of manufacturing process of the liquid crystal display panel by the conventional liquid crystal dripping and panel pasting method.
Similarly with the case of the liquid crystal filling method, first, by using a printer, provide coating of solution of polyimide on a surface of the TFT substrate and also on a surface of the counter substrate, then performs pre-baking using heating equipment such as a hot plate oven or an IR oven. After pre-baking, performs main baking for carrying out heating dehydration condensation of the polyimide coating film, and forms the alignment layer of uniform thickness (S810, S820).
After carrying out pre-baking and main baking and forming the alignment layer of uniform thickness, rubbing process for the respective alignment layers on both substrates is to be performed by a rubbing roller which rubs over the surface of the alignment layer in a same direction by a rubbing cloth (S811, S821).
And in order to remove the residue on a surface of a substrate, washes both substrates and makes them dry (S812, S822).
Next, using the screen printing method or the dispenser drawing method, forms the seal patterning with the ultraviolet curing resin or the heat curing resin on one of the substrates of the pair, (it is assumed that the TFT substrate is used for this substrate as an example), and after this, an AG coating is applied (S813, S814).
Spray spacers, such as polymer beads or silica beads, on the other substrate (a counter substrate) of the pair substrates by a spacer sprayer with a wet type method or a dry type method, and makes them fix (S824). Then, necessary amount of the liquid crystal is dripped in a viewing area surrounded by the seal material of one substrate (here TFT substrate) using a dispenser for liquid crystal dripping under ordinary pressure (S815).
Next, after fixing spacers on the counter substrate and dripping the liquid crystal on the TFT substrate respectively, the panel alignment is performed for both the substrates of the pair, and pastes them together (S830).
Then, the pair of substrates pasted together is pressed from both outsides, the seal material is to be crushed, and a desired gap between two substrates is formed. After this, the ultraviolet ray is glared from rear side of the substrate (here TFT substrate) for pre-curing the seal material (S831), then bakes at predetermined temperature for actual curing the seal material (S832). And, cuts the substrates of the pair in a predetermined portion of the outside of the seal material (S833), and the liquid crystal display panel is formed.
Thus, the liquid crystal display panel manufactured as above controls display indication by the liquid crystal sandwiched by the gap between the substrates of the pair pasted together. Therefore, if air bubbles mix into the liquid crystal, the thickness of the liquid crystal layer will change and display fault will occur.
As a method for improving an occurrence of the display fault which is caused by such air bubbles, there is the technology disclosed in JP,9-80452,A, for example. The manufacturing method of the liquid crystal device which performs a degassing treatment (vacuum treatment) for removing the gas currently mixed into the liquid crystal composition is disclosed in JP,9-80452,A. This method realizes the degassing treatment prior to carrying out the liquid crystal filling process by leaving the liquid crystal composition as is under the pressure environment below an atmosphere. By performing such vacuum treatment, residual moisture, gas constituents, etc. causing air bubbles are removed from the liquid crystal.
However, it is also to be considered that not only as for residual moisture or gas constituents but solid-state components such as dusts cause the display fault, and hereafter, solid-state component other than the composite of the liquid crystal calls a foreign substance.
In manufacturing the liquid crystal display panel using the liquid crystal filling method mentioned above, even if foreign substances, such as dusts, mix in the liquid crystal, it does not become a problem because a foreign substance having a size more than a diameter of a hole of liquid crystal filling port for pouring a liquid crystal is removed.
However, in manufacturing the liquid crystal display panel by using the liquid crystal dripping and panel pasting method, since the liquid crystal is directly dripped on a substrate, foreign substances mixed into the liquid crystal will be incorporated in a gap as they are. And when the foreign substance of size, which cannot be disregarded compared with the gap between the substrates, is mixed, display faults, such as a bright defect (what is also called a luminous dot) by which a bright dot is recognized visually, will occur, and it causes the problem of low display quality and the low yield in manufacturing.
On the other hand, the method of performing filtration treatment which removes foreign substances in the step of mixing and refining the liquid crystal composition using the filter of a predetermined bore diameter is disclosed, for example, by JP,11-131063,A, JP,2003-322836,A.
However, even if foreign substances were removed by the filtration treatment at the time of a liquid crystal refinement, foreign substances may newly mix in other process of the liquid crystal manufacturing, such as a delivery examination at the time of delivering the refined liquid crystal, a step which subdivides a liquid crystal into small containers for transportation, and a step which packs the subdivided containers. In work environment, foreign substances may also mix in some processes of manufacturing the liquid crystal display panel, such as a step of transfer the liquid crystal from subdivided container to another container for liquid crystal dripping, a step of a vacuum treatment, and a step of a liquid crystal dripping step.
Thus, the method of manufacturing the liquid crystal display panel of high quality is required, in which the foreign substances which may be mixed in the manufacture process of the liquid crystal, or the manufacture process of the liquid crystal display panel are assuredly removed for manufacturing the liquid crystal display panel which sandwiched the liquid crystal to the substrates of the pair.